1. Field of the Invention
The present invention relates to an intelligent cartridge for plug-compatable use in conjunction with a printer to improve and accelerate printer operation and a method of image processing therefor, and more particularly to an intelligent cartridge for plug-in reception in a page printer to function as an accelerator in processing of page description language (PDL) and other such data into image data for printing.
2. Description of the Prior Art
Page printers, such as laser printers, have been quickly and widely marketed in recent years and are rapidly becoming the leading device for high-speed data printout from computers. The resolution of a laser printer is typically between 240 to 800 dpi and the most recently developed laser printers can easily print several pages per minute. These printers principally utilize an electrophotographic printer, such as, a xerographic unit having a photosensitive drum as part of its print engine. A laser printer starts printing after storing in memory image data for each page to be printed since the process of printing is continuous through various stations or processes, such as, photoreceptor charging, exposure, toner application and toned image transfer, consecutively executed in synchronism with photosensitive drum rotation, as is well known in the art. Therefore, the capacity of the memory for image data development in a page printer must be sufficiently large to provide for image data of a single page. If image data compression is not available, the memory capacity is fixed by the resolution and the available paper sizes. For example, to print on paper 8 inches in width and 10 inches in length with a resolution of 300 dpi, the total number of the pixels involved may comprise 8.times.10.times.300.times.300=7,200,000, so that the required memory capacity necessary would be 0.9 Mbytes.
A data image processor typically program data of a page description language (PDL), such as, PostScript.RTM. (PostScript.RTM. is a registered trademark of Adobe Systems, Inc.), may be received in addition to character code data and bit image data. A character code process may be utilized to convert character code data and/or graphic image data into bit image data according to a font pattern stored in the font memory and thereafter storing the data in a bitmap memory and a PDL process for converting print data into image data according to a program of the PDL and storing the converted data in a bitmap memory as a bit image of the image to be printed upon spooling and presentation to the page printer engine.
If print data received from an computer is a bit image of the image to be printed, the printer receives the data to printed and sequentially stores the data. The processing speed depends primarily on and is limited by the data transmission speed. Parallel data transfer, such as, Centronics specification data transfer, is comparatively fast, and, thus, there are few situations where the data transfer speed is below that of the xerographic unit print speed capability.
However, in a case where a printer functions to receive information such as character codes, character size, and character and line pitches as print data and to develop or process the data into a printable image, or in the case where a printer receives a program described in PDL as print data and, thereafter, interprets the data for development and processing by calculating and generating a bit image according to the print data to be printed, the accomplishment of the entire process to completion of image printing is much slower than compared to a simple bit image transfer. In other words, the printer processing speed is limited primarily by the capacity of the operating CPU of the printer and its memory access time, which is much lower than the printing capacity of the xerographic unit per se. As an example, in a case of a page printer which can print 10 pages per minute, the time allowable for preparing the image data for printing each page is no more than 6 seconds. To develop all 0.9 Mbytes of data, the processing time allowed for each byte is as short as 6.67 microseconds (6 seconds/0.9 Mbytes). This processing speed is hardly capable of being accommodated by even a high-speed RISC-type processor. On the other hand, most xerographic units have a print capacity of 10 pages per minute. Thus, the processing capacity of the controller for processing print data into bit image data is an obstacle toward the improvement of printing speed, particularly for present day or existing printers.
The internal memory capacity of some present day page printers are expandable. An example of a memory cartridge for use with a printer is disclosed in U.S. Pat. No. 4,872,091. Also, some page printers have expansion slots to improve the function by attaching one or more cartridges in which fonts or printing programs are stored such as disclosed in U.S. Pat. No. 4,908,637. The font cartridge can be adapted to operate with designated CPU programs in the printer controller but the performance of using the expanded font capability of the printer is limited by the hardware design already existing in the printer. Also, expandable applications are effective in improving the processing speed of the printer by expansion of the printer memory capabilities but they cannot improve overall image processing capacity. Since the buffer between the cartridge and the printer controller is a read-only buffer, matters concerning image processing are left to the printer controller. For example, there is known the employment of an IC cartridge to provide another kind of page language interpreter program in order to enhance functional operation of a printer by means of processing with another PDL and supporting program contained in a ROM in the cartridge, which PDL is not already internally provided in the page printer. The cartridge stores the program in a mask ROM and is inserted into an expansion slot of the printer. In the case of such a printer cartridge which supplies another page language interpreter program, a printer controller reads a specified address location allocated to a cartridge such as immediately when the power is turn on to the printer. If the attached cartridge contains a particular page description language program, a predetermined code is sent back by the printer controller indicating the controller's recognition that the cartridge has an acceptable page language program for operating in conjunction with the printer. The control of the printer is transferred to the interpreter program stored in the cartridge. As a result, the printer can interpret the print data received from an external device according to its particular page language. However, the processing speed is not significantly improved and the total printing speed is often reduced due to the employment of a different, high level page description language.
It is an object of this invention to provide an intelligent cartridge for a printer, in particular, a page printer, wherein the total print capacity is improved and accelerated in spite of the employment of different page language interpreter programs or different high level page description languages.